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MILES O'BRIEN, CNN ANCHOR: Hello, I'm Miles O'Brien. Welcome to CNN PRESENTS: THE COLUMBIA IS LOST, four words, seven astronauts, one tragic fate. The space shuttle disaster has shocked and saddened us all. The nation and NASA continue to mourn and we continue to ask so many questions but there are so few answers about Columbia's final minutes, about its initial launch. Here at NASA they know one thing, in order for a mission to succeed it has to be very nearly perfect.

A couple of years ago I had an opportunity to see what happens in the months that lead up to a launch, to see how people prepare a space shuttle orbiter for flight. It is a tense and harrowing time and the people responsible for getting a shuttle ready realize they have very little margin for error.

(BEGIN VIDEOTAPE)

UNIDENTIFIED MALE: This is shuttle launch control at T-minus two hours, 31 minutes, 25 seconds and counting.

UNIDENTIFIED MALE: (UNINTELLIGIBLE).

O'BRIEN (voice-over): It seems so familiar.

UNIDENTIFIED MALE: They are all reporting that they are go for launch. All elements are reporting in.

O'BRIEN: So predictable.

UNIDENTIFIED MALE: At about 7:40 a.m. today the crew woke up. They were served breakfast at around 8:00 a.m.

O'BRIEN: A crew of astronauts, anonymous to most of us.

UNIDENTIFIED MALE: People stopped being able to recognize things like that.

UNIDENTIFIED MALE: This is not easy to do. You almost have to turn yourself into a pretzel to get in.

O'BRIEN: The launch team plugged in.

UNIDENTIFIED FEMALE: Do you want to set up for continuous monitoring?

UNIDENTIFIED MALE: Yes, we're going to need to.

O'BRIEN: And vigilant.

UNIDENTIFIED FEMALE: Your (UNINTELLIGIBLE) is complete. I have three day (UNINTELLIGIBLE).

O'BRIEN: The milestones passing like, well, clockwork.

UNIDENTIFIED MALE: At T-minus three hours and holding this is...

UNIDENTIFIED MALE: Counting, less than one hour on the countdown.

O'BRIEN: It all looks so routine.

UNIDENTIFIED MALE: Well, they've been training as a crew for almost three years.

O'BRIEN: A ritual I knew by rote or so I thought.

O'BRIEN: The beanie cap is actually the gaseous oxygen vent hood. From my perch on the press mound not far from the pad, I've confidently told the world about the latest departure of humans from our planet. It's my job. It doesn't have the little twirly thing on the top.

(on camera): I was cocky enough to think I knew the drill but now I know different. I asked the folks at NASA if they would show me what really happens between the launches, and after a good deal of convincing they agreed to open up the hangar doors. For ten months, we followed one orbiter every step of the way as she was prepared for flight, and now I know how little I knew about what it takes to launch a shuttle.

UNIDENTIFIED MALE: Get ready to rock and roll guys.

O'BRIEN: Thirty years after it was first envisioned it is still an icon to American technological prowess.

UNIDENTIFIED FEMALE: Youngstown, it was beautiful.

UNIDENTIFIED MALE: Somebody wrote a problem report on this.

O'BRIEN: But beneath the surface it is a vehicle riding on borrowed time.

GENE NURNBERG, SHUTTLE FLOW MANAGER: I said them vendors don't even make that stuff anymore. The airlines don't fly that old junk anymore.

UNIDENTIFIED MALE: Well, we should work a little quicker. O'BRIEN: It was sold on the promise it would deliver cheap and easy access to space but has never come close.

UNIDENTIFIED MALE: This is called a SNERT.

O'BRIEN: A SNERT?

UNIDENTIFIED MALE: Right. That means schedule never equals real time.

O'BRIEN: Remaining a finicky beast that demands attention like a spoiled child.

UNIDENTIFIED MALE: I think it's going to have to come off back there first.

O'BRIEN: It is understood well by the people who make it fly.

UNIDENTIFIED MALE: (UNINTELLIGIBLE).

O'BRIEN: And yet they live in fear of its secrets, its hidden flaws.

UNIDENTIFIED FEMALE: I think in the back of everyone's mind they're always thinking, you know, if something happens at the last minute will we be able to recover?

O'BRIEN: Twenty years ago they predicted it would be in the Smithsonian by now and yet it flies on and on with no replacement in sight and it is left to a handful of dedicated people to keep it going, knowing anything less than perfection means disaster. What scares you the most about the job?

MIKE CECARLO, TECHNICIAN: Screwing up.

O'BRIEN: This is their story. We begin where we normally leave off, at the end of a shuttle mission.

UNIDENTIFIED MALE: I got 304, 304, 304 all the way around.

UNIDENTIFIED MALE: Discovery copies. Go for the burn.

UNIDENTIFIED MALE: I'm going to the burn card.

O'BRIEN: December 27, 1999, welcome to the flight deck of the Space Shuttle Discovery, 15 years old, on her 27th voyage, 119 circumnavigations of the globe behind her.

UNIDENTIFIED MALE: OK.

UNIDENTIFIED MALE: Houston, we have the runway in sight.

O'BRIEN: Little more than an hour after the crew nudged Discovery out of orbit over the Indian Ocean, they were knocking at the door at home on the shores of the Atlantic.

UNIDENTIFIED MALE: Ten feet at 192, (UNINTELLIGIBLE). Shoots coming.

UNIDENTIFIED MALE: Post landing guys. Do me one favor let's not lose our concentration here and screw it up at the last minute. This is when everybody kind of gets silly.

O'BRIEN: The convoy crew started rolling even before Discovery's long deceleration petered out but the ground crew draws near with a healthy dose of caution.

UNIDENTIFIED MALE: You got to go for your safety assessments.

O'BRIEN: An orbiter is brimming with a witch's brew of toxic, hazardous chemicals and explosives.

UNIDENTIFIED MALE: We have the possibility of encountering hazardous gases and vapors of hydrogen, ammonia, (UNINTELLIGIBLE).

O'BRIEN: Like a critical patient just wheeled into an emergency room, Discovery is quickly attached to life support, umbilicals that purge hazardous gases and keep the crew and equipment from overheating.

GREG KATNIK, NASA ENGINEER: I am here as part of the orbiter landing recovery team and specifically my job is to get the big picture.

O'BRIEN: NASA Engineer Greg Katnik spends much of his tarmac time scrutinizing the heat deflecting and insulating tiles that cover much of the orbiter. Without them, the aluminum skin that lies beneath would become soup during the 2,300 degree reentry.

Katnik counts 153 dings, 24 of them an inch or larger. Overall, Discovery fared well during her three million mile journey with one big exception. A tile is missing on the right wing, on a flat called an elevon.

O'BRIEN: It is only one of Discovery's 24,000 tiles and yet its void quickly becomes a focal point.

UNIDENTIFIED MALE: You don't need them all. It happens every now and then. Well, we don't like losing them.

O'BRIEN: But that's more false bravado than technical reality. Astronaut Scott Kelly (ph) and everyone else here knows the loss of a single tile in a critical location means disaster.

UNIDENTIFIED MALE: We like to fly a perfect vehicle, so we're going to find out why it happened and check it and make a change if we need to.

O'BRIEN: A perfect vehicle.

UNIDENTIFIED MALE: If you operate all three switches, verify it off.

O'BRIEN: A million parts, 230 miles of wires.

UNIDENTIFIED MALE: All three helium interconnects, verify GPC (ph).

O'BRIEN: One thousand sixty plumbing valves and connections, all of it must be perfect. Three miles down the road lies a gleaming, spotless, climate-controlled hangar, Orbiter Processing Facility 1, the OPF, the tailor made womb where the orbiter will be nurtured back to readiness for another flight. It's a glove fit, only an inch of leeway in any direction.

UNIDENTIFIED MALE: Still about a half inch off. You got to come back to the left, Bob. Slow it up. Slow it up. Slow it up. (UNINTELLIGIBLE) right there. Making a close (UNINTELLIGIBLE) guys.

O'BRIEN: Discovery's long journey in space is over. Discovery's long journey back to space has begun.

UNIDENTIFIED MALE: We're there. That's it.

UNIDENTIFIED MALE: Ready, here comes one.

O'BRIEN: Coming up...

UNIDENTIFIED MALE: I got this side, Ray.

O'BRIEN: A mechanic's nightmare.

UNIDENTIFIED MALE: The first time I had sweaty palms and I'm like we need to put this down. I have to put this down right now.

(COMMERCIAL BREAK)

O'BRIEN: It's just a scosh (ph) after four o'clock and Gene Nurnberg is up and already restless to get at the job that has consumed him for 40 years. Gene Nurnberg started out here readying Apollo spacecraft for moon shots. More than 20 years ago he got the first space shuttle Columbia ready for her first flight. Today, he is still at it.

GENE NURNBERG: I don't care that I haven't been promoted in 35 years. I already got the best job in the world literally. If you're here early enough they haven't done this distribution yet. Here's the master log if you really want to find out what happened last night.

O'BRIEN: He manages what NASA calls the flow.

NURNBERG: They call me dad just to tweak me. That feels kind of good. You got to keep it as tightly orchestrated as you can.

O'BRIEN: The 1.2 million step minuet.

NURNBERG: Let me show you something.

O'BRIEN: Of maintenance, refurbishment.

NURNBERG: They get refurbished every flight.

O'BRIEN: Repaired, checked.

NURNBERG: We discovered some tarnished blankets.

O'BRIEN: Double checks and still more checks.

NURNBERG: We have a criteria that says after eight flights you change it.

O'BRIEN: That render a space shuttle ready for another ride.

NURNBERG: Let's go on up here a minute.

O'BRIEN: Most days, he begins with a solitary hangar tour, a walk around up, over, and through the multi-tiered maze of scaffolding that envelops Discovery.

NURNBERG: It's not complicated rocket science but you do need to kind of keep track of all of the things that are going on.

UNIDENTIFIED MALE: It's not rocket science, huh?

NURNBERG: No, just this thing and that thing and keep it in order. That's not rocket science. What time is it?

O'BRIEN: The wee hours walk around serves him well. As he retreats to the offices upstairs...

NURNBERG: I am late. We are late. We just started this five minutes ago.

O'BRIEN: ...where Discovery's day is choreographed in a series of meetings that grow larger as the clock unwinds.

NURNBERG: I thought he was going to look at taking that off with buckets but I don't -- when he looks, I don't think he wants to do it anyway. We will do the APU connect skate tomorrow, good job though. That tape trick was nice work between you and the shop guys.

O'BRIEN: It might surprise you to know there are only a few NASA supervisors on this team. Most everyone in this room works for the space agency's prime shuttle contractor, the United Space Alliance, USA.

UNIDENTIFIED MALE: What we're working right now is we have (UNINTELLIGIBLE) blankets.

O'BRIEN: It's a joint venture of aerospace giants Boeing and Lockheed Martin. Since 1996, NASA has paid USA $1.1 billion a year to keep the shuttle fleet flying.

UNIDENTIFIED MALE: And we will not pull the pressure down with the radiators in the position that they're in. We'll wait until that issue is behind us.

O'BRIEN: But nothing comes easy or fast where the rubber meets the road in the 30,000 square foot climate-controlled orbital processing facility.

UNIDENTIFIED MALE: We have to go around that way.

O'BRIEN: From stem to stern, the good ship Discovery presents all kinds of obstacles for the hands on workforce.

UNIDENTIFIED MALE: I'm going to get you a good view. It's the best you can do in here.

O'BRIEN: Mike DeCarlo (ph) is on the team that works beneath Discovery's tail.

MIKE DECARLO: You're going to be in the tightest spot in here just to get the bolts out of this thing.

O'BRIEN: Step into his office, the aft compartment and you are instantly privy to the world view of a mouse under the hood of a car.

UNIDENTIFIED MALE: It can stand on anything yellow. The struts, like these struts are OK. You can -- they're pretty strong.

O'BRIEN: This is clearly the business end of Discovery where the three main engines are attached and where a lot of other critical components live, hence the plumbing and wiring spaghetti.

UNIDENTIFIED MALE: It's a lot of monkeying around in here when you got to get something done in here as you can see the way we crawled back in here.

UNIDENTIFIED MALE: Right here. I got it. Everybody get out and get in position.

O'BRIEN: The innocuous looking piece of hardware they are removing is an auxiliary power unit, a crucial device that keeps Discovery's controls running during landing, the price tag for a new unit, $3 million.

UNIDENTIFIED MALE: The first time I had sweaty palms and I'm like we need to put this down. I got to put this down right now.

UNIDENTIFIED MALE: That's what they call the pizza plate.

UNIDENTIFIED MALE: I'm happy for you.

UNIDENTIFIED MALE: This is the stand it will just sit on. It makes it easier to handle. This is the aft bay five. The (UNINTELLIGIBLE) in and out. It wasn't meant to be worked on like we do. I really -- I don't think the engines were designed to come out as often as they do and a lot of other things. It's not mechanic friendly.

O'BRIEN: At the other end of the orbiter in the forward shop, spacecraft operator Lisa Davis would second that motion.

LISA DAVIS, SPACECRAFT OPERATOR: My first impression was that it was a lot smaller in size than I thought, you know, from what I'd seen on TV and pictures.

O'BRIEN: Here they do windows, the old-fashioned way.

UNIDENTIFIED MALE: We try to do it every ten, 15 minute segments.

O'BRIEN: The forward windows used by the commander and pilot get between 60 and 80 hours of elbow grease to remove the haze left by rocket plumes during launch, the goal give the crew the clearest possible view of the runway at mission's end.

UNIDENTIFIED FEMALE: It is very labor intensive but it does work.

UNIDENTIFIED MALE: Four, 3, 2, 1, liftoff.

O'BRIEN: Liftoff of the 25th space shuttle mission. The day the old way was the worst way.

UNIDENTIFIED MALE: Challenger go with throttle up.

UNIDENTIFIED MALE: That's the first thing that went through my mind was my God I hope it's nothing that we did on the pad.

(COMMERCIAL BREAK)

O'BRIEN: If you like rare birds this is the place to be. Ringed by fences, aggressively patrolled for trespassers, and beyond the reach of Florida's relentless developers, the 140,000 acre Kennedy Space Center is a safe haven for all sort of endangered species.

In fact, skimming through the maze of waterways that slice through the (UNINTELLIGIBLE), it's easy to forget where you are and then in an instant you are reminded. Looming 525 feet above the water the Vehicle Assembly Building, one of the largest buildings on the planet, built during the space race to hold four of NASA's might moon ships.

Today it is the nexus of a small city of hangars, offices, labs, and workshops built to coddle the rarest birds of all, NASA's quartet of space shuttle orbiters.

UNIDENTIFIED FEMALE: I'm going to say yes and I'll verify that.

UNIDENTIFIED MALE: That's your final answer?

UNIDENTIFIED FEMALE: That's my final answer.

O'BRIEN: Colleen Adams (ph) knows what it's like to be a rarity.

UNIDENTIFIED FEMALE: Being a female is always difficult. I mean when you're in a working environment this is basically a male dominated field.

O'BRIEN: After 17 years of hard work and hard knocks in and around space shuttles...

UNIDENTIFIED FEMALE: You've got to be good at what you do and march forward.

O'BRIEN: She is one of Gene Nurnberg's chief lieutenants, and as such is the highest ranking woman in the orbiter processing facility.

UNIDENTIFIED FEMALE: We have training classes, a lot of training classes.

O'BRIEN: She's in charge of the so-called mid body, the shuttle's payload bay.

UNIDENTIFIED FEMALE: You tape and tether your glasses. You don't want your glasses falling down into the orbiter.

O'BRIEN: This time around her job is to pack Discovery's trunk with some new pieces for the budding space station.

UNIDENTIFIED FEMALE: And he's looking into it.

O'BRIEN: She spends a good part of her day angling for resources, navigating a complex maze of competing chores.

UNIDENTIFIED FEMALE: Do you guys have anything that's portable? You got a second? I don't know if it's one or two. This is the hardest part, pulling it all together and saying you're done. Thank you very much.

O'BRIEN: Spend a little time with Colleen and you wonder how anything ever gets done in this Byzantine world.

O'BRIEN: To get procedures changed so she could repair a part in a lab across the hall she had to round up a dozen signatures. That seems a little excessive.

UNIDENTIFIED FEMALE: Well, I think it's more everybody wants to know what's happening with the equipment. If you weren't in a time constraint it would be great because this is like a tool.

O'BRIEN: It is the most heavily used tool of all.

UNIDENTIFIED MALE: The paper trail.

O'BRIEN: Whatever the action, every precisely prescribed step of the way there is a reaction of signatures and stamps on detailed checklists, first by the lead workers, then by a quality inspector from shuttle contractor United Space Alliance, and then if it's a critical piece of flight hardware a NASA inspector also buys the paper, as they say, the running joke a shuttle is considered ready for launch once the stack of paperwork would stand just as high as the rocket.

UNIDENTIFIED FEMALE: We're working it until it goes away and when it goes away that will be a good thing.

RON DITTEMORE, SHUTTLE PROGRAM MANAGER: After Challenger, we put a whole bunch, we put a lot of layers into the system to protect ourselves and those layers were necessary because we found a lot of weaknesses in our process and we probably overcompensated for it.

O'BRIEN: Slowly but steadily, Discovery's secrets peel away as technicians remove panels and pieces large and small. Beneath the orbiter, the thermal protection team is busy inspecting, tagging, patching, and replacing damaged tiles.

UNIDENTIFIED MALE: So we drill them off, snap the head off, then drive the rest of the rivet back in.

O'BRIEN: Technician Dennis Heathner (ph) sets up shop beneath Discovery's right wing. He begins repairing the bare aluminum that was scorched after the missing tile came loose.

DENNIS HEATHNER, TECHNICIAN: The paperwork is very intense. In an eight-hour day we'll work six hours of paperwork to get two hours of work done.

O'BRIEN: While Dennis works...

UNIDENTIFIED MALE: They're the kind of use that only an engineer can love I guess.

O'BRIEN: ...some shuttle gumshoes are all over the case of the missing tile.

UNIDENTIFIED MALE: We always have to worry about some kind of debris hit on the vehicle that actually impacted a tile and fractured it and caused it to fall off. That's what we're really worried about.

O'BRIEN: It is Greg Katnik's job to pour through the reams of high speed close-up movies that capture Discovery's fiery trip to orbit in stunning detail.

KATNIK: Here's another interesting feature. We watched the body flap and you can see that there's a little bit of movement to it. You've actually got to treat everything on the vehicle like it is the most significant part of the vehicle. You never know when the smallest thing might end up being the most catastrophic. I mean whoever thought a simple little "O" ring inside a booster would do what it did?

O'BRIEN: It was a leaky "O" ring that sparked the Challenger explosion. UNIDENTIFIED MALE: So one little tile and one little location actually has far reaching consequences and causes us to go actually do a very big investigation.

O'BRIEN: But the engineering films do not capture a smoking tile, if you will, leading Katnik to surmise it probably fell off during Discovery's return from space.

KATNIK: As long as I don't see anything square with straight edges tumbling that might be a tile everything looks good.

O'BRIEN: Across the street at the place where they make those tiles, engineer Mark Gray (ph) is doing an experiment to see how the tile was bonded to Discovery's skin. The missing article is one of the larger, more complex tiles, a problem child.

MARK GRAY, ENGINEER: What concerns us is that if this one had been maybe four or five tile in front of it and around the hydraulic lines we might be talking about a whole other scenario today. You're talking about basically the astronaut crew not being able to make it back home.

UNIDENTIFIED MALE: We do maintain a large inventory of the materials that we need.

O'BRIEN: Martin Wilson is the man in charge at the thermal protection system facility. Here they mix, bake, mill, and coat about 1,000 tiles a year to keep the shuttle fleet flying.

UNIDENTIFIED MALE: This is what...

O'BRIEN: That's the raw material? That's what you get.

UNIDENTIFIED MALE: This is the raw material.

O'BRIEN: The ceramic tiles are made mostly of silica, essentially highly refined sand.

O'BRIEN: What's the temperature in there right now, Mark?

GRAY: Three hundred.

O'BRIEN: They shed heat faster than a speeding shuttle, safe to touch a few seconds after they come out of a 2,200 degree kiln.

UNIDENTIFIED MALE: What does it feel like?

UNIDENTIFIED MALE: Hot.

O'BRIEN: High maintenance as they may be they are probably the single greatest technological achievement of the shuttle program.

UNIDENTIFIED MALE: To be honest you have to give credit to the people in the '60s and '70s who actually invented this stuff that nobody up to this point has really come up with anything better.

O'BRIEN: Which is an amazing statement when you consider the history of the space shuttle. Was the shuttle way ahead of its time?

CHRI KRAFT, FORMER NASA MANAGER: No, on the contrary. I think we used the technology that we had in the '70s to build that machine and we were conservative.

O'BRIEN: Because they had to be. Former flight director and manager Chris Kraft was there, still lording over the Apollo missions when the grandiose gold plated ideas for what next began circulating.

UNIDENTIFIED MALE: There are 38 main thrusters.

O'BRIEN: Many hope for a three-pronged approach and missions to Mars staged at a space station orbiting the earth built and serviced by a reusable spacecraft.

UNIDENTIFIED MALE: The United States can no longer afford the luxury of the throw away rocket. Our answer to this challenge is the space shuttle, the world's first reusable spacecraft.

UNIDENTIFIED MALE: That wasn't in the cards so the management of NASA decided well, what can we do? What will the budget allow?

O'BRIEN: It allowed for only one idea at a time. NASA had no choice. Without a vehicle to get humans off the planet, the rest of the plan was academic, so NASA managers started making some big promises. They pitched it as a machine that could operate like an airliner, a flight every two weeks, cheap, easy, even profitable access to space.

UNIDENTIFIED MALE: And I think it was overly aggressive and I think we were overly optimistic about what the amount of things that were going to fly in space, but I think that, you know, that's what it took to sell it.

O'BRIEN: It was a road to ruin for NASA. The agency tried desperately to live up to its own hype, launching shuttles at a frenetic pace.

UNIDENTIFIED MALE: We have SRB ignition. We have ignition now of the solid rocket boosters and liftoff. Liftoff. Liftoff. The shuttle has cleared the tower.

UNIDENTIFIED MALE: My controllers here are looking very carefully at the situation, obviously a major malfunction.

O'BRIEN: And then 73 seconds after the 25th shuttle launch, the Challenger exploded, shattering the myth of easy access to space.

ADAMS: That's the first thing that went through my mind was my God I hope it's nothing that we did on the pad.

O'BRIEN: The shuttle program would never be the same.

UNIDENTIFIED MALE: We have a report from the flight dynamics officer that the vehicle has exploded.

O'BRIEN: And neither would the people who were there.

NURNBERG: I felt like going back to that just because it was so traumatic and because you know some of those guys personally. I don't think about it as much as I probably should.

UNIDENTIFIED MALE: Clear, I'm looking at -- checking with the recovery forces to see what can be done at this point.

ADAMS: We all watched it. America watched it. Everybody saw it and it's like you go, you got to be careful. It's worth it.

O'BRIEN: When we come back, pushing the shuttle to the limit.

KRAFT: You're going to run out of spares. You're going to run out of people that are building the hardware and the hardware will become extremely expensive to build because it's a one time thing.

(END VIDEOTAPE)

(COMMERCIAL BREAK)

(NEWSBREAK)

(BEGIN VIDEOTAPE)

O'BRIEN (voice-over): Astronauts may get all the glory but they sure don't have the market cornered on risk in the space business. Mike DeCarlo is suiting up for the harsh environment on the ground inside the space shuttle Discovery.

DECARLO: Tight fit, no fuel or nothing gets past the glove.

O'BRIEN: He is donning, ever so methodically, a SCAPE suit, a seemingly dyslexic acronym for Self Contained Atmospheric Protective Ensemble.

UNIDENTIFIED MALE: Well, the blue ones we call Gumby suits.

UNIDENTIFIED MALE: Gumby. You want me to turn this way. No leaks.

O'BRIEN: SCAPE is the mandatory dress code whenever orbiter technicians work on parts of Discovery that contain hypergolic chemicals, meaning they instantly explode when mixed. It's a clever, reliable way to fuel rocket thrusters in space but a real nightmare to work with on the ground. How do you do any work in this suit?

UNIDENTIFIED MALE: We can do it.

UNIDENTIFIED MALE: The bottom line is exposure can kill you. That's why we wear these suits. O'BRIEN: During this SCAPE operation the crew will install a new auxiliary power unit. It means working on some plumbing that might carry traces of hydrazine, a highly toxic, corrosive, hypergolic chemical.

UNIDENTIFIED MALE: Just went a little too much.

O'BRIEN: If NASA had its way this scene would not be happening at all. The agency would like the money to replace the old hydrazine power units with state of the art batteries, no special attire required.

As a matter of fact, there is a long wish list of upgrades to some of the shuttle's most antiquated, high maintenance systems, and there are plenty of them. The shelves at the supply depots are (UNINTELLIGIBLE) with 1970s technological time capsules. It's a big problem for shuttle program manager Ron Dittemore.

DITTEMORE: Every day is another opportunity because something's awry, something's amiss, a part broke, needs analysis.

O'BRIEN: NASA built its shuttle fleet to last 400 missions. Initially, the agency expected to log those flights in ten years, but two decades later the orbiters still have more than 300 flights left in them. They're running a marathon with a sprinter's strategy.

DITTEMORE: Up to this point it's been kind of a very short term approach. Make the decisions you need to make to fly for five years and that's very difficult to do. You only work on things that you can solve and implement in a five year span.

O'BRIEN: But now, more than 20 years after the first shuttle launch, the concepts for a new vehicle remain just that. The problem plagued X-33, touted as a forerunner for a shuttle replacement, was killed before it ever got off the ground. It's now dawning on NASA the shuttle fleet will likely fly another 20 years but that won't be easy or cheap.

KRAFT: You're going to run out of spares. You're going to run out of people that are building the hardware and the hardware will become extremely expensive to build because it's a one time thing.

O'BRIEN: And yet NASA veteran Chris Kraft says NASA's four orbiters could be flown more aggressively.

KRAFT: The same thing you do in a 747. When it lands, it goes through an automatic check out system to determine what systems are working and what systems aren't, and if something's not working you replace it and then you go fly it. You got the best information on the performance of the system of the shuttle, of the orbiter, when it lands. All you have to do it fill it up and go again.

DECARLO: It wasn't designed to be taken apart every flow that I know of. I think there's places that we shouldn't go and shouldn't do anything with unless it's broke. DITTEMORE: One way to do it, Miles, is to just say I'm not going to look. I'm just not going to look and I hope everything goes OK. I don't think that's a wise steward.

O'BRIEN (on camera): The stewards of the shuttle fleet are conservative because they have to be. Every time they launch they assume the entire program is on the line and it probably is.

A program that at one time was judged on whether it could meet its own unrealistic launch schedule now really only has one thing to prove, that it is not taking too many risks and that, more than anything else, serves as a governor over what happens as the calendar and Discovery and her components move toward a launch date.

(voice-over): The solid rocket boosters are carefully inspected. The huge blimp like external fuel tank is hoisted into place. The three main engines are removed and inspected in a gleaming engine shop.

UNIDENTIFIED MALE: Pull it up a little further Joe.

O'BRIEN: The million dollar toilet is gingerly hoisted into place, the landing gear cycled, and after months of painstaking preparation, a new tile is glued onto that wing flap. After combing through the old paperwork, engineers determine workers used the wrong size liner when they attached the tiles six flights ago. This is good news as there is no reason to suspect a problem that would ground the fleet, and suddenly it occurs to me that pile of paperwork might be worth its weight.

Nearly nine months after she came home to roost, Discovery is ready to leave the orbiter processing facility. It's a milestone moment, slightly bittersweet for the OPF crew.

ADAMS: When we start understanding how the whole thing operates, it becomes a lot more than an orbiter or just a piece of equipment. It become something exciting, you know. You're watching it launch and you receive it back and, you know, you get to go through this process. You can see where it got hurt on its journey, you know, and you get to repair it. So, it turns into, you know, a living entity.

O'BRIEN: Coming up, it takes a lot to make a shuttle fly but not much at all to keep it on the ground.

UNIDENTIFIED MALE: I found something I don't like.

(END VIDEOTAPE)

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O'BRIEN: Bolted on to the six million pound rock crushing crawler, Discovery begins a three mile saunter to Launch Pad 39A, her departure point from earth. A machine that travels six times faster than the speediest rifle bullet never exceeds the pace of a stroll on the beach on the ground. Now that Discovery is standing on end, attached to her tank and boosters, exposed to the elements, the preparation puzzle reaches a new degree of difficulty.

UNIDENTIFIED MALE: Remember guys, this is something developing right now.

O'BRIEN: Jim Bovara (ph) is the man in the hot seat when the shuttle world pivots from horizontal to vertical. With three weeks left before launch they are warily watching a hurricane in the Atlantic. Should it dogleg toward the cape, Discovery would have to fall for cover, creating a quandary for Bovara.

JIM BOVARA: What we're looking at is integrating a schedule that's moving forward preparing the vehicle for launch and protecting a schedule that allows us to move it back off the launch pad and so some of those activities are at odds with each other.

BOVARA: I'm basically looking at we might have to factor in a little SCAPE operation. I'm not the boss. I'm the conductor. You know the orchestra is paid much more than I am. I just kind of point to the brass section, point to the strings, that's it.

UNIDENTIFIED MALE: There are no launch window cutouts in this launch window.

O'BRIEN: Meanwhile, the team that orchestrates the countdown and makes the final decision to light Discovery's candles, sits down and plugs in.

UNIDENTIFIED MALE: OK, I copy that.

O'BRIEN: To hone their skills.

UNIDENTIFIED MALE: Currently that leak out in the storage area is stable at 1.4 percent. We're not going to take any action until it reaches three percent.

O'BRIEN: It's a hair raising simulated countdown in the firing room. It's more than just a drill. They must endure this SIM to be certified for the real thing.

UNIDENTIFIED MALE: We are currently in a no-go state for IPR 5.

UNIDENTIFIED MALE: Everything is inserted. We got the safing problem inserted, the abort problem is inserted.

O'BRIEN: Next door, a small team of gremlins, led by engineer Mike Chinelli, is conjuring up all kinds of simulated mischief. Several serious simultaneous failures for the launch team to contend with.

CHINELLI: Oh, it's real. I feel it and they feel it. I mean like I said it's a simulation but when you're into it, it's real, and you realize you're practicing because one day you might be doing that for real.

UNIDENTIFIED MALE: Is there any further troubleshooting you're going to be requiring of the crew?

UNIDENTIFIED MALE: You want to make sure you get it right now so when it does happen in real life, if it does, you're ready for it and you do it right that time.

O'BRIEN: Cue the flight crew and the crescendo begins. The seven astronauts who will fly to the space station on Discovery drop in from Houston for some dress rehearsals.

UNIDENTIFIED MALE: Five thousand, good radar.

UNIDENTIFIED MALE: Radar.

O'BRIEN: Commander Brian Duffy (ph) and pilot Pam Melroy (ph) practice steep dives to the shuttle runway in a Gulf Stream business jet rigged to handle like an orbiter.

UNIDENTIFIED MALE: The last thousand feet before landing I was trying to minimize my input.

UNIDENTIFIED FEMALE: Three hundred.

UNIDENTIFIED MALE: I was working to get it set up to land, get it right where I wanted it, get it set up to land and then let it land.

O'BRIEN: The entire crew goes to the pad to practice a scenario no one would like to see, a major failure on the ground that forces an emergency evacuation.

UNIDENTIFIED FEMALE: Three, two, one, go.

O'BRIEN: They practice releasing, though not riding, the slide wire baskets designed to whisk them off the 195 foot level in a hurry. This is the crew's only speedy passage to safety. Space shuttles are not equipped with ejection seats or any kind of automatic crew escape system. They get a quick tour of the blast proof bunker at the end of the line.

UNIDENTIFIED MALE: It's important for us if there are any injuries on anybody to get that information to them.

O'BRIEN: And, some tips of driving their getaway tank.

NURNBERG: I think there's an overall awareness of what we're doing and the risk involved that we think about, that the people think about. I mean it's not, you know, there's no escape system. There's no bail out.

O'BRIEN: As time draws near, the hurricane has now passed and the preparations at the pad do not break stride.

DECARLO: We got the 02 meter. We can verify that with that camera.

O'BRIEN: A big piece of the space station, a truss that will support the station's solar panels is loaded into the payload bay. Inside the crew module the cupboards are carefully stocked and the entire stack is rigged with explosives, the self destruct system that would be used as a last resort if Discovery veered violently off course forcing ground controllers to blow up the rocket and all onboard.

UNIDENTIFIED MALE: Power switch is on. Ready light is on.

O'BRIEN: Near the end of this long, arduous, careful process, there remains a deep undercurrent of anxiety. Discovery is layered with backup systems for her backup systems but everyone here knows the score. NASA estimates 1,660 scenarios where a single failure would cause the catastrophic loss of the vehicle and crew.

DITTEMORE: Because of Challenger, there's a certain mindset that is very risk averse. In fact, a whole culture has grown up that wants to minimize the risk in everything we do to the point where they would like it to be zero risk. Well, zero risk would paralyze you.

O'BRIEN: As it is, it doesn't take much to paralyze a shuttle. Discovery's crew is suited up and on the way and her fuel tank is boiling over with super cold liquid oxygen and hydrogen, and so the ice men cometh.

Greg Katnik's ice team is on the prowl for chunks of ice that might damage Discovery during launch but they're also looking for anything that doesn't look right. In short, after months and months of painstaking work, it is the final inspection.

UNIDENTIFIED MALE: Oh, oh I found something I don't like.

O'BRIEN: It's a three-inch pin lodged on a strut far from easy reach.

UNIDENTIFIED MALE: This is going to be significant, isn't it?

UNIDENTIFIED MALE: I wouldn't say significant but I have to deal with it.

UNIDENTIFIED MALE: You can not assume that a little eight-ounce pin will get away Scot free.

DITTEMORE: The damage to an engine or the body flap could be severe and because we did not want to take that risk we decided to scrub.

O'BRIEN: Two hundred and eighty-seven days after Discovery came home, she would wait at least one more day to fly away. Day 288, October 11, 2000.

UNIDENTIFIED MALE: In summary, we have no LCC violations, no ORS violations and no IPR conditions. Discovery looks ready to go.

UNIDENTIFIED MALE: And they'll begin final preparations to ingress space shuttle Discovery for the second time.

NURNBERG: The biggest difference between then and the '60s, that first launch and now is somehow I don't cry any more.

UNIDENTIFIED MALE: And these are people that as a matter of course every couple of months put everything on the line and there's a lot on the line.

UNIDENTIFIED MALE: Standing by for burnout and separation of the twin solid rocket boosters.

UNIDENTIFIED MALE: OK it slips away, a little bit of a roll out from it.

ADAMS: I always wait that 60 seconds after the launch. You can see the booster falling. It's like the crowd quiets. It's very, very emotional.

UNIDENTIFIED MALE: About 25, 30 seconds (UNINTELLIGIBLE).

DITTEMORE: And you watch those first two minutes and you watch that contrail go up into the sky lit by the sun and the solids separate and you see those main engines going off into the distance. That's the poetry of the process.

UNIDENTIFIED MALE: Excellent. Excellent.

UNIDENTIFIED FEMALE: Congratulations.

UNIDENTIFIED MALE: We got the weekend off. That was nice. Look, there they are guys.

UNIDENTIFIED MALE: Welcome to space and congratulations.

UNIDENTIFIED MALE: Houston, it was beautiful.

UNIDENTIFIED MALE: OK, Calvin. Get it back on the ground. Christmas is coming. We got a lot of stuff to do.

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O'BRIEN: The loss of Columbia has grounded the space shuttle fleet for now but President Bush has vowed to continue sending astronauts into space and continue the exploration of the high frontier because, as he put it, it is not an option we chose. It is a desire written in the human heart. That's it for this edition of CNN PRESENTS. I'm Miles O'Brien. Thanks for joining us.

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